US1912337A - Condenser induction motor - Google Patents

Description

y 1933- c. KENNEDY 1,912,337

CONDENSER INDUCTION MOTOR Filed Dec. 28, 1929 2 Sheets-Sheet 1 ll iinJJ jfeniar mwe @rW y 30, 1933- c. L. KENNEDY v 1,912,337

CONDENSER INDUCTION MOTOR Filed Dec. 28, 1 929 2 Sheets-Sheet 2 (D N 0 0 7 e9 (-9 (D 0 ea ea "69 CD i m 6) (D G) & 9 6; a) (D 6D (D G) 69 G) a Q 69 (D n L ea @i 69 ea' fi ea ea 3 ea ea m ea {Y w N G) 65 l 0) (D GD K (D CD L G) 0 L (D G) (D a) J CD 2 w k 3 E Mine. )6 I fl Maw L" Patented May 30, 1933 I UNITED STATES PATENTOFFICE CARLTON L. KENNEDY, OI BRAINTREE, MASSACHUSETTS, ASSIGNOR TO THE HOLTZEB- CABOT ELECTRIC COMPANY, OF MASSACHUSETTS IRDXBURY, MASSACHUSETTS, A CORPORATION OF CONDENSER INDUCTION MOTOR Application filed December 88, 1929. Serial 1T0. 417,199.

The present invention relates to condenser induction motors.

The objects of the present invention are to provide a condenser'induction' mot-or having provision for operation at a plurality of speeds primarily b changing the number of poles; to accomplis the pole changing operation with a minimum 0 external connections; and to provide for satisfactory starting torque on any of the connections.

With these objects in view, the resent invention comprises the condenserin uction motor hereinafter described and particularly defined in the claims.

In the accompanying drawings, Fig. 1 is a diagram of the preferred form of motor connected for the smaller number ofpoles; Fig. 2 is a diagram of the motor shown in Fig. 1 but connected for the larger number of poles; Figs. 3, 4 and 5 are diagrams of a modified form of motor shown connected respectively for high, medium, and low speeds; Fig. 6 is a diagrammatic development of a portion of the stator windings of the motor as connected for the smaller number of poles; and Fig. 7 is a diagrammatic development similar to Fig. 6 but as connected to produce the greater number of poles.

The illustrated embodiment of the invention makes use of a change in polarity of a part of the windings of the motor to' change the number of poles and therebyto change the speed. The motor shown in Figs. 1 and 2 isa two-speed motor having permanent internal connections and only three external connections, which latter may be arran ed to cause the motor to run at either a'high or low speed by altering the number of poles.

The motor, shown in Fi s'. 3, 4, and 5 is similar to that of Figs. 1 an 2 in that it provides for high and low speeds by changing the number of poles and also for an intermediate speed by increasing the slip while maintaining the smaller number of poles. In this motor, an extra external lead is required, although the internal connections are permanent. 7

Before describing the connections of the two forms of motors, the operation of p010 changing by reversal of polarit of part of the win ings will be explained y reference to Figs. 6 and 7. The stator is here shown 'as provided with two main windings 6 and dicating an instantaneous current coming out toward the reader, and the plus signs an instantaneous current goin away from the reader. In Fig. 1, each 0 the main windings 6 and 8 .is shown as distributed over one pole of the motor. \Vith the currents flowing as shown in Fig. 1, the winding 6 forms a north pole and the winding 8 a south pole. The condenser winding 10 forms a north pole displaced 45 from the north pole formed by the main winding 6 and similarly, the condenser winding 12 is displaced 45 from the main Winding 8, the complete spread between adjacent poles of opposite polarity being 180. By merely reversing the polarities of the main winding 8 and the condenser operate at approximately one-half its former speed. Taking 180 electrical degrees as the displacement between a north pole and a south pole, it will be seen that the condenser windings 10 and 12 are respectively displaced from their corresponding main windings by an angle of The resent invention is and 90 for the two connections, but in any case, it will be noted that the displacement between the main andcondenserwindings is twice as great for the connection 'for the not limited to the exact isplacements of 45 I greater number of poles as for the smaller number of poles. The diagrams of Figs. 6 and 7 are intended to show only a stator develo .ment for only a single pair of poles for t e high speed connectlon. and two pairsof poles for the low speed connection, but obviously, the windings ma be extended to produce any number of pairs of poles.

The motor diagrammatically shown m Fi .1and2isatwoed lech mo tzr having but three e terniil leadsw main windings 6 and 8 are permanently connected to ther and the condenser circuits which inc ude the condenser windings 10 and 12 respectively are closed on themselves. The condenser circuits include the condensers 14 and 16 in series with their respective condenser windings 10 and 12. For convenience, the ends of the winding 6 are designated as a and b, and those of winding 8 as c and d, those of the condenser winding 10 as e and f, and those of the condenser winding 12 as and h. The ends 6 and c of the main ings 6 and 8 are connected to ther and to a common external lead 18. T e 22 connect to points a and d. and e and the points (1 and h are connected.

For the high-s ed connection, as shown in Fig. 1, the lea s 20 and 22 are connected by a wire 24, and line voltage is impressed between the leads 18 and 20. The motor then operates with the smaller number of poles. The currents in the several winding: are indicated by arrows, although it is to understood that the arrows indicate the relative directions of currents only and do not indicate the phase dis lacements which exist tween the main an condenser wind: For lowed operation, the connections are made as 'own in Fig. 2. The line voltage is impressed between the leads 20 and 22, t a lead 18 being then inactive. N 0 changes in the internal motor connections are necessary.

uming, for example, that the motor is wound for four poles in the high-speed connection, the motor will have a synchronous speed of 1800 R. P. M. The displacement between the condenser and main windings is electrical degrees. Each condenser circuit, being short-circuited by the connection 24, can receive no direct energization from The points a permanently the line voltage and'the only voltages which en'st in the condenser circuit are induced voltages caused by links of flux from the main windings and by t rotor. The first of these voltages induced in the condenser windin is ap roximately in phase with the line voftage, while the second voltage is dis laced approximately 45 electrical degrees rom the of these voltages, namely, that induced flux linkages from the main windings, is equivalent to a transformer action and exists even when the rotor is stationary. Therefore, the motor has a start torque due to currents in the main and con enser windings which are di laced both in time and space from each er; Thus, even though line voltage is not. directly impressed upon any part of the condenser circuits, a sufiicient voltage exists by induction to aflord a satisfactory starting torque and also to permit leads 20 and In e rotation of the ins voltage. The first b by be ing condenser winding. The

satisfactory condenser running speeds.

For the low-speed connection shown in I'Ti 2, the number of poles is increased to ergi tand the chronous speed therefore is re need to 900 P. M. It will be noted that the main windin s, instead of being in parallel as for the igh-speed connection, are now in series. This change from parallel to series connection, in increasing the number of poles, is necessary as in all pole changing motors to maintain the main flux densities substantially constant. The voltages existing in the condenser circuits are quite different from those of the high-speed connection. asmuch as the condenser windings are now displaced electrical degrees from the main windings, there is no voltage induced by transformer action although a voltage 90 out of phase with the line voltage is induced in'the condenser windings h the rotation of the rotor as the motor speeds up. At starting, however, there is no induced voltage of any kind in the condenser windings, but inasmuch as the condenser nected directly across the line, sufiicient currents are caused to flow through the condenser circuits to produce a starting torque.

ese currents are out of phase with the main winding currents because of the reactance of the condensers. Inasmuch as full line voltage is now impressed upon each condenser circuit, a starting torque comparable to the starting to ue for the high-speed connection is obtain d.

It will be seen that for the high-speed connection which gives the smaller number of poles starting torqfiie is afforded by the inu voltages in t e condenser circuits and not at all by any voltages directly impressed upon the condenser circuits, whereas with the low-speed connection, the conditions are reversed, the startin torque being afforded by the direct application of the line voltage to the condenser circuits and not at all by any induced voltages in the condenser windings. These totally different startin torque conditions are brought about b identical internal connections, the only c anges necessary being changes in the three external leads.

As a feature of the motor above described, attention is called to the connections wherey no excessive voltages exist at any time tween a main winding and its correspondoints a and e of the main and condenser win in s 6 and 10 are directly connected together and d and h of the windings 8 and 12 are connected together. Inasmuch as the windings motor operation at 6 and 10 carry currents in the same general direction which also holds true for the wind- 8 and 12, there is at no point between a main winding and its condenser winding an sufiicient to break down the is of importance when it is excessive voltage insulation. This circuits are conill) considered that the main and condenser windin s are laid in the same slots of the stator.

he motor shown in Figs. 3, 4 and 5 is simi lar in its electrical characteristics to the motor described above and differs from it only in that an extra external lead is brought out and that by proper combinations of the fourleads, three speeds may be obtained. For the high and low speeds, the connections are similar to those shown in Figs. 1 and 2, the change from high to low speed bein efi'ected by doublingt 6 number of poles. he intermediate speed" s" also obtainediby a series connection of the main windings without reversal of polarity, whereby the increased slip of the motor under load is availed of to produce a speed abouth'alf-way between normal high and low speeds of the rotor.

The main windings 6 and 8, the condenser windings 10 and 12,. and the condenser-s14 and 16 are as for the motor shown in Figs. 1 and 2. The same letters to indicate the ends of the respective windings are used as iu t-he first case. A lead 20 connects with the po nts a and e of the windings 6 and 10, another'external lead 26 connects with the oint 'c of the main winding 8, and also with its associated condenser circuit. The points 9 and b are permanently connected together and to an external lead 28, while the point d is permanently connected to the condenser 14 and also to an external lead 30. These are the permanent connections which are not required to be changed.

For the high speed connection of Fig. 3, the leads 20 and 30 are connected together as indicated at 32 and the loads 26 and 28 are connected together as indicated at 34.

' Line voltage is impressed between the leads 20 and 26. The main windings 6 and 8 are now in parallel and they carry currents in such relative directions as/to produce the smaller number of poles; Each condenser circuit is completely short-circuited on itself. All of the connections are electrically identical to those of Fig. 1, and the motor operates in exactly similar fashion.

For the middle speed connection of Fig. 4, the leads 28 and 30 are connected together and the voltage is impressed between the leads 20 and 26 as before. The windings 6 and. 8 now carry currents in the same directions as for'the connections for Fig. 3, but the windings are now in series instead of parallel. Both condensercircuits are also in series and are connected across the line. The number of poles is unchanged, because there is no reversal of polarity of an winding. The effect of connecting the windin in series is to reduce the voltage impresse on each main winding, while maintaining the number of poles" the same. The magnetic flux density is decreased and the slip is increased. The slip may be approximately five times the slip obtained for t e high-speed connection and motion may assuming a normal slip of 5% for the-hi h speed connection at full load, the slip for t 6 middle speed connection will be a proximately 25%. The full load speed or this connection is therefore about 1,350 B. P. M. Because of the lar' e slip, the intermediate speed will undergo uctuations upon changes of load, which are proportionately greater than the fluctuatiors of speed'for the high speed connection. It will be noted that starting torque is afforded both by direct application of line voltage to the condenser circuits and also by voltages induced in the condenser windings b flux linkages from the main windings. The condenser windings are displaced from the main windings by 45 electrical degrees as in the high speed connection. 1

The low speed connections are as shown in F i 5. [he leads 28 and 26 are connecte at 34 and the line volta e is impressed between the leads 20 and 30.. a he main windings 6 and 8 are therefore connected in series but with reversed polarity so that the number of poles is doubled, ivin a synchronous speed of 900and a fulfload operatin speed of about 855 R. P. M. In view'of t e fact that the number of poles is doubled when the series connection is used, the flux densities will be approximately the same as for the high speed connection and normal slips will obtain. The condenser circuit including the winding 12 and the condenser 16 is complete- 1 short-circulted on itself and inasmuch as t e condenser winding is displaced 90 from the main winding, no voltage is induced in this condenser winding at starting. The condenser winding 12 is therefore ineffective to produce any starting torque. Thecondenser circuit including the condenser winding 10, however, is directly connected across theline. The fact that this condenser circuit has fullline voltage impressed upon it compensates for the inactivity of the condenser winding 12 at starting. It has been found that with this connection, a starting torque about equal to the startin torque of the high-speed conobtained.

It will be seen that the present invention provides a condenser induction motor adapted for operation at either twoor three speeds with a minimum of alteration of connections. In no case is a change in internal connections required. For the two-speed motor, only three external connections are employed and for the three-speed motor, only four external connections are necessary. An chan es in speed are readily. effected by simple a terations in these external connections.

Having described the invention, what is claimed is:

1. A condenser induction motor having, in combination, two main windings connected together, two condenser circuits each associated with the main windings and connected across both main windings, each condenser circuit comprising an auxiliar winding and a condenser, a single external ead connected to the point of connection of the main windings, and a pair of leads connected to the 6 opposite ends of the main windin 2. A condenser induction motofiiaving, in combination, two main windings two condenser circuits associated therewith, each including an auxiliar winding and a series 10 condenser, each con enser circuit being connected between an end of one main winding and an end of the other main winding, a connection between the main windings, an external lead connected to said connection, and

external leads connected to the remaining ends of the main windings.

3. A condenser induction motor having, in combination, two main windings, two condenser circuits associated therewith, each in- 9,0 cluding an auxiliar winding and a series condenser, each con enser circuit being connected between an end of one main windin and an end of the other main winding, an four leads connected respectively to the ends of the main windings.

4. A condenser induction motor having, in combination, two main windings, two condenser circuits associated therewith, each including an auxiliary winding and a series condenser, a lead connected to one end of a main winding and one end of each condenser circuit, a second lead connected to one end of the other main winding and the remainin end of each condenser circuit, and a third lead connected to the remaining ends of both main windings.

5. A condenser induction motor having, in combination, two main windings, two condenser circuits associated therewith, each including an auxiliary winding and a series condenser, one condenser circuit being connected between an end of one main windin and an end of the other main winding, an the other condenser circuit being connected between the remaining ends of the two main windings, and four leads connected respectively to the ends of the main windings.

In testimony whereof I have signed my I name to this specification.

1, 50 CARLTON L. KENNEDY.

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